Method and apparatus for selective processing of captured images

ABSTRACT

Methods and apparatus are disclosed for identifying intended response marks in an optically scanned image of a response sheet having key marks and response targets printed in the same color. Pixel darkness values assigned by a digital imaging scanner are used to locate key marks and response targets and to identify response marks. Areas of the sheet may be selectively filtered to mask the response targets. Alternatively, a color imaging scanner may be used to produce a set of color values, such as RBG values, for each pixel. Software can act as a virtual filter by using the RBG values to detect or to mask a color in the image.

RELATED APPLICATIONS

[0001] This application claims a priority filing date based uponprovisional patent application Serial No. 60/224,327, filed Aug. 11,2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to the general field of optical scanningto collect data and digital images from documents, and within that fieldto the more specific field of scanning wherein the colors printed on asheet may be selectively processed so that key marks and responsetargets may be printed in the same color. Although the methods andapparatus described herein may be useful in other related tasks, themost common usage is likely to be in the processing and scoring ofstandardized assessment tests, and particularly for OMR (Optical MarkRecognition).

[0004] 2. Description of the Prior Art

[0005] Traditional OMR processes, in which respondents place marks onforms or sheets, require that such forms be manufactured to preciselycomply with very tight design tolerances. Most response sheets for usewith traditional OMR systems have targets printed, typically in theshape of a circle, with a special ink to show respondents where to makemarks. This special ink absorbs little or no light in the spectrumprocessed by the optical system, instead reflecting it to the scanningcamera in close to the same intensity as a white area of the sheet. Ifno response mark is made in the target area, the scanning systemproduces a pixel image of the area as not having any mark, just as ifthe paper were blank throughout the area Many OMR systems use the red orinfrared spectrum for processing and red ink for the targets, since thered ink highly reflects incident light in the infrared spectrum whilepencil marks highly absorb the infrared light.

[0006] Sophisticated OMR systems also use key marks for location andorientation, including a special form of key marks known as timingtracks that indicate the scanning speed by the distance between trackmarks in the image. These key marks are printed in a second ink,typically black, that highly absorbs light in the appropriate colorspectrum and therefore can be recognized and processed by the opticalsystem. The ink used to print key marks may also be used to print othermarks to identify the type of form and/or to identify the particulardocument. The various inks used for the targets, and other inks used forkey marks and identification marks, are well known in the art. However,the requirement of using two separate inks on the same form and thedegree of printer control necessary to ensure that the two inks areproperly in register of each other makes OMR form printing an exactingand expensive process.

[0007] An advantage exists, therefore, for an optical scanning methodand apparatus capable of OMR processing of sheets that have responsetargets and key marks printed in the same color. This would allow theresponse sheets to be printed on less expensive printers and with lessexacting print control.

SUMMARY OF THE INVENTION

[0008] This invention provides methods and apparatus for selectivelyprocessing colors printed, by machine or by hand, on a response sheet sothat the same color may be used to print key marks and response targetsfor OMR or similar processing. The selective processing may be performedusing a physical hardware filter to select the colors being processed indifferent segments of the sheet by the scanner, or by using software toselectively process colors by selectively interpreting color values,such as red, green, blue (RGB) values, assigned by a full spectrum colorscanner.

[0009] One embodiment uses a physical filter element located in relationto the form to selectively filter a portion of the form during scanning.A response sheet may have response targets and key marks printed in thesame color ink, with one section of the form containing the key marksand another section containing the response targets. The section of theform containing the key marks will be unfiltered and processed by thescanner in the normal fashion. That is, unfiltered white light will beabsorbed or reflected off the section containing the key marks so thatthe section is processed by the scanner and assigned pixel darknessvalues within a gray scale, usually 0 to 255. In a second section of thesheet containing the response targets, a filter is positioned betweenthe light source and the scanner's sensor so that the light incident onthe second section is the color of the response targets. therebyrendering the response targets unreadable in that section. The grayscale values in the key mark section are used to locate the key marks inthe captured image which, in turn, can be used to project the locationof the response targets areas, but only a mark in the response areas,made by the respondent in a color other than the color of the responsetargets, will show up as dark pixels.

[0010] Another embodiment uses software to selectively process capturedimages from response sheets having key marks and response targetsprinted in the same color. There are currently available digital imagingscanners capable of capturing an image of a response sheet with pixeldarkness values assigned for three color bands, usually the primarycolors red, green and blue (some may use the complimentary colors cyan,magenta, yellow). The assigned pixel darkness values for each of thethree colors to each pixel enables a software program to recognize thecolor of each pixel. This can be used to provide a virtual filter whenscanning a response sheet that has key marks and response targetsprinted in one color. The scanner captures a digital image of the sheethaving RGB darkness values assigned for each pixel. That is, each pixelwill have a pixel darkness value for red, blue and green. Then using thedarkness value that corresponds to the color of the key marks, thesystem locates the key marks in the captured image. From the key marks,the system can locate, or project an expected location of, the responsetargets in the image. Then, using the darkness value of another color,the system can identify an intended response mark at the expectedlocation of a target without processing the darkness value of the targetitself.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a flow chart of the method steps for using a physicalfilter to perform OMR on a sheet having key marks and response targetsprinted in the same color.

[0012]FIG. 2 is a schematic diagram of a physical filter arranged toperform selective filtering of a sheet being scanned by an opticalscanner.

[0013]FIG. 3 is a schematic diagram of the method steps for usingsoftware to selectively process colors when performing OMR on a sheethaving key marks and response targets printed in the same color.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENTS

[0014] Throughout this specification the terms “sheet” and “form” areused interchangeably, and both refer to a document containing one ormore areas for a person to respond to a question or instruction bymaking a mark in an appropriate location on the document. OMR forms forstandardized testing are common, but not exclusive examples. Asdescribed earlier, these forms may contain printed marks for location,orientation, determination of scanning speed, or document identificationby the scanner. These marks will be referred to herein as “key marks”,with the understanding that the term includes, in its broad sense,timing tracks and any other type of mark utilized to process, orient,identify and interpret response sheets by optical scanning.

[0015] When reading this specification, reference is made to the colorsof the visual spectrum. While black is technically not a color, butrather the absence of all color, when the term “color” or “visualspectrum” is used, it is considered to include black. Similarly, whiteis also not technically a color, but rather the presence of all colors,and is also deemed to be included when reference is made to the term“color” or “visual spectrum.”

[0016] While the invention described herein will work with non-whitesheets, white sheets are used for purposes of describing the inventionin this specification.

[0017] The invention is described herein in different embodiments toenable one skilled in the art to make and use the invention. No attempthas been made to describe all of the possible embodiments.

[0018]FIG. 1 shows the sequence of steps utilized in the embodimentwherein a physical filter is used to perform selective processing duringoptical scanning of an OMR form on which response targets and key marksare printed in the same color. Such a form, for example, might have redkey marks in the form of timing tracks along a side margin of the form,and red response targets in areas of the form inboard of the sidemargin.

[0019] The first step (10) is to provide a digital imaging scannerhaving a light source and sensor for detecting light reflected off thesheet. The scanner should also be capable of assigning pixel darknessvalues within the gray scale to the amount of light reflected fromdiscrete areas (pixels) of the sheet. Such scanners are well known, andusually provide a gray scale value to the various colors printed on asheet from 0 (no reflected light or “black”) to 255 (“white”). Thecolors of the visible spectrum are each converted to shades of gray andassigned a unique value between 0 and 255. For example, when a red, blueor green mark is detected by a scanner, the scanner will assign a grayscale value to the mark of somewhere between 0 and 255.

[0020] In a following step (20), a color filter is provided that isappropriate for the color ink used to print the key marks and theresponse targets. The filter may operate through absorption, reflection,scattering or other principle, but its function is to filter the whitelight emanating from the scanner so that the light directed onto thesheet (where the filter is positioned so that light is filtered beforereaching the sheet) or reflected off the sheet (where the filter ispositioned so that light is filtered after reflecting off the sheet) isthe same color as the key marks and response targets. The result is thatthe marks having the same color as the light that passes through thefilter are not distinguishable from the sheet itself.

[0021] In the next step (30), the filter is arranged in a particularrelation to the sheet path through the scanner, such that lightreflected from a section of the form containing key marks is notfiltered, and light reflected from the response targets is filtered. Inthe example above, the filter may be placed such that the light isfiltered to allow red light to be incident on the section containing theresponse targets, while white light is allowed to be incident on themargin where the timing tracks or key marks are located. The red keymarks will absorb the green and blue components of white light andappear red. The scanner will then convert the red to a shade of gray andassign pixels corresponding to the key marks a relatively low gray scalevalue indicating a darkness. The sheet will reflect the red light andshow up in the images as pixels with gray scale value closer to white,enabling the scanner to accurately detect the key marks. In the sectioncontaining the response targets, however, the red light causes the redresponse targets to appear the same as the white paper, while any othercolor marks made by the respondent will appear black.

[0022] Thus, the sheet is scanned (40) with the digital imaging scannerto produce pixel darkness values for the pixels in the captured digitalimage of the sheet by assigning a gray scale value to each pixel. Thegray scale values are used to locate (50) key marks in the capturedimage. Then in a following step (60), the location of key marks in theimage is used to locate or project an expected location of responsetargets in the captured image. An expected location of a target may bedetermined from the specification for the sheet and the variations fromthe specification of the key marks in the image, as described in pendingPCT application PCT/US01/16966, the specification of which is herebyincorporated by reference.

[0023] In a following step (70), the gray scale values of pixels in anarea at the locations calculated to be the expected locations of eachresponse target are processed to identify response marks. If a blue,green or black response mark is present, it will appear dark, and if noresponse mark is present, it will appear light. Although the responsetargets are printed in the same color as the key marks, the filter isarranged so that the response targets appear to be the same as the sheetand are ignored.

[0024]FIG. 2 shows how an optical scanner can be modified by placing afilter in an orientation that leaves one edge of the sheet exposed tounfiltered light, while the remainder of the form is exposed to filteredlight. A filter (110) is placed between the scanner's light source (112)and its camera or light-sensing device (114). The filter covers most,but not all of the width of the sheet (116) being scanned and willgenerally correspond to the section of the form having response targets.A light barrier (118) may be added to make a sharp separation of thefiltered and unfiltered light.

[0025] Using a red filter as an example, the filter (110) may freelypass light in a red band, but absorb or otherwise block thetransmittance of other visible light. Then a form (116) can be printedwith key marks and response targets in red. The side margin (120) of thesheet that receives unfiltered light from the source (112) can be usedas the location of key marks, since, red ink will absorb green and blueband components of the unfiltered white light and appear dark in theimage, enabling the scanner to assign it a gray scale value that isdistinguishable from the sheet.

[0026] The response targets are printed in the selectively filtered area(122) of the sheet, where the filtered red band light reflected off thered ink will be approximately the same as is reflected off the whitepaper, causing them both to have approximately the same gray scalevalue. Marks made by a lead pencil, blue pen, green pen, or other suchmark that absorbs red light will cause such marks to appear dark in theimage and be distinguishable by their pixel darkness values. Thus, theselective placement of a red light filter enables a scanner to read thered key marks in the unfiltered section while ignoring the red responsetargets of the filtered section.

[0027] When a selective filter is added to a scanning system asdescribed above, the filter will generally reduce the total light in thefiltered area. Consequently, it may be necessary to compensate byreducing the amount of light in the unfiltered area so that thereflected light reaching the scanner's light sensor is roughlycomparable over the form.

[0028] Referring now to FIG. 3, an alternative to selective filteringwith a physical filter is to use software in conjunction with a colorscanner to selectively process the colors within a captured image. Inthis embodiment, the various colors present on a sheet are assigned asset of pixel darkness values in the primary or complimentary colors.This set enables a software program to selectively process particularcolors in particular sections of the sheet. For example, where key marksand response targets are printed in red, the software may be programmedso that the color red is processed in the section of the form having redkey marks, while only colors other than red are processed in the sectionof the form having response targets. Although the response targets areprinted in the same color as the key marks, the software is arranged sothat the response targets appear to be the same as the sheet and areignored.

[0029] The first step (1000) of FIG. 3 is to provide a digital imagingscanner capable of capturing an image of a response sheet with a set ofcolor values, such as a set of RGB values, assigned to each pixel. Sucha scanner records and assigns pixel darkness values for the threeprimary colors, red, green, and blue for each pixel on the sheet.Collectively, those values can be referred to as a pixel's RGB values.(The term “RBG values” should be understood as a shorthanded expressionfor primary or complimentary color values; so the complimentary colorvalues would still be referred to as RBG values.) In the case of redink, the RGB values would show a high red content and a low content forblue and green. Green ink would have a high green content and low forred and blue. Blue ink would have a high blue content and low red andgreen. A white pixel will have high content for all three primarycolors, whereas the RGB value for black marks will have low content forred, green and blue. Examples of scanners capable of properly assigningRGB values range from the HP ScanJet 5100C up to the SCAMA 000 byInoTec.

[0030] As in the physical filter alternative described above, thesoftware embodiment allows the key marks and response targets of aresponse sheet to be printed in the same color ink, while providing evengreater flexibility in the amount of colors which may be properlyprocessed as response marks. Step (2000) of the process shown in FIG. 3is to provide a response sheet having key marks and response targetsprinted in the same color. That color may be any color in the visualspectrum, including black (or white where a non-white form is used).However, the color selected for the key marks and response targets maynot be used by a respondent to make response marks. That is, if blue isused for the key marks and response targets, blue may not be used tomake response marks. For this reason, red may be the color of choice forthe key marks and response targets because then any color other than redmay be used to make response marks including black pencil, black ink,and blue ink.

[0031] In a following step (3000), the scanner captures a digital imageof the sheet with RGB values assigned to each pixel that corresponds tothe color of that pixel. Then, using the RGB values for the color of thekey marks, the key marks are located in the captured image (4000).

[0032] The next step (5000) is to calculate, based on the location ofthe key marks in the image, an expected location of response targets inthe image. Then in the following step (6000), the RGB values thatcorrespond to the color of the response targets are ignored. Theexpected target locations are interrogated to determine the presence ofRGB values that correspond to any color other than the response targetcolor. Accordingly, any mark in any color other than the response targetcolor made at an expected target location may be properly processed asan intended response.

[0033] In this embodiment, computer software is used to selectivelyprocess colors on a response sheet using the color's RGB values enablingthe key marks and targets to be printed in the same color. The scannercalculates pixel darkness values for red, green and blue so as toprovide RGB values for each pixel to locate key marks in the capturedimage. Based on the location of the key marks, the software calculatesan expected location of response targets. The software then processesthe RGB values provided by the scanner in any color other than the colorof the response targets to identify the presence of marks made by arespondent at the expected location of a target. Again, those marks maybe made in any color other than the color of the response targets.

[0034] While the present invention is quite capable of scanning a sheethaving key marks and targets printed in two colors that are in closeregistration, implementation of the present invention enables the keymarks and response targets of response forms to be printed in the samecolor ink or in two colors not in close registration with each other.Selective processing also facilitates the use of printers that are notcapable of keeping two or more colors in close registration for printingresponse forms. Examples of such devices include single color printingpresses, digital duplicators, mimeograph machines, and other devicesthat can print only one color at a time.

[0035] Although embodiments of the invention have been described indetail, it is to be understood that the invention is not limitedthereto, and that various changes can be made therein without departingfrom the spirit and scope of the invention, which is defined by theattached claims.

What is claimed is:
 1. A method of identifying intended response marksin an optically scanned image of a response sheet having responsetargets printed in areas of the sheet apart from a section of the sheetcontaining key marks, the key marks and response targets being printedin the same color, the method comprising the steps of: (a) providing adigital imaging scanner having a light source and sensor for detectinglight reflected off the sheet, the scanner being capable of assigningpixel darkness values so that each pixel is assigned a gray scale value;(b) providing a color filter in the color of the key marks and responsetargets, (c) arranging the filter in relation to the sheet as it passesthrough the scanner such that light reflected from the sectioncontaining key marks is not filtered and light reflected from theresponse targets is filtered, (d) scanning the sheet with the digitalimaging scanner; (e) using the gray scale values to locate key marks inthe captured image, (f) calculating from the location of the key marksin the image an expected location of response targets in the image, (g)using the gray scale values to identify an intended response mark at theexpected location of a target.
 2. A digital imaging scanner forperforming optical mark recognition (OMR) of a response sheet havingresponse targets printed in areas of the sheet apart from a section ofthe sheet containing key marks, the response targets and key marks beingprinted in the same color, the scanner comprising: a) a light source; b)a sensor for detecting light reflected off the sheet; and c) a filterdisposed between the sensor and the light source so that the lightreflected off the key marks is not filtered and light reflected off theresponse targets is filtered.
 3. A method of identifying intendedresponse marks in an optically scanned image of a response sheet havingkey marks and response targets printed in the same color, comprising thesteps of: (a) providing a digital imaging scanner capable of capturingan image of a response sheet with RGB values assigned to each pixelcorresponding to the color of that pixel, (b) providing a response sheethaving key marks and response targets printed in the same color, (c)capturing with the scanner a digital image of the sheet with each pixelhaving RGB values assigned thereto, (d) locating key marks in thecaptured image by processing pixels having RGB values that correspond tothe color of the key marks, (e) calculating from the location of the keymarks in the image an expected location of response targets in theimage, (f) processing pixels having RGB values corresponding to anycolor other than the color of the target to determine whether anintended response mark was made at a response target.
 4. A method as inclaim 3, wherein the response sheet has key marks and response targetsprinted in red.
 5. A method of performing optical mark recognition (OMR)with a digital scanner, said method comprising the steps of: (a)providing a digital imaging scanner capable of capturing an image of aresponse sheet with RGB values assigned to each pixel corresponding tothe color of that pixel, (b) providing a response sheet having aplurality of response targets printed in the same color, (c) capturingwith the scanner a digital image of the sheet with each pixel having aRGB value assigned thereto, (d) using RGB values that corresponds to thecolor of the targets to locate response targets in the captured image,(e) using RGB values that corresponds to any color other than the colorof the target to determine whether an intended response mark was made ata response target.
 6. A method as in claim 5, wherein the response sheethas response targets printed in red.
 7. A system for identifyingintended response marks in an optically scanned image of a responsesheet having key marks and response targets printed in the same color,comprising: (a) a digital imaging scanner capable of capturing an imageof a response sheet with RGB values assigned to each pixel correspondingto the color of that pixel, (b) computer software capable of processingthe RGB values that correspond to the color of the key marks to locatekey marks in the captured image, (c) computer software capable ofcalculating from the location of the key marks in the image an expectedlocation of response targets in the image, (d) computer software capableof processing the RGB values that correspond to any color other than thecolor of the target to identify an intended response mark at theexpected location of the target.
 8. A system as in claim 7, wherein theresponse sheet has key marks and response targets printed in red.
 9. Asystem for performing optical mark recognition (OMR), comprising: (a) adigital imaging scanner capable of capturing an image of a responsesheet with RGB values assigned to each pixel corresponding to the colorof that pixel, (b) computer software capable of using RGB values thatcorrespond to the color of response targets on the sheet to locateresponse targets in the captured image; (c) computer software capable ofusing RGB values that correspond to any color other than the color ofthe target to determine whether an intended response mark was made at aresponse target.
 10. A system as in claim 9, wherein the responsetargets are printed in red.